TOL- I think that PuhLease meant the same thing as the person who said that NCSY is like the Parah Aduma – it’s metaheir the temaim and metamei the tehorim. In other words, they do great work bringing not-Frum people close to Yiddishkeit (and in some cases perhaps in inspiring jaded Frum kids) but some Frum kids end up less Frum as a result.
In her case, it sounds like she specifically meant the people who work for NCSY – that they become less Frum. The broom represents the people working for NCSY -they are making the floor clean (helping others become Frum) but they get dirty in the process.